The invention relates to a device for measuring the contact force between a contact wire and a pantograph of an electrically-powered vehicle. More particularly, the present application relates to a device for measuring the contact force between a contact wire and a pantograph of an electrically-powered vehicle, particularly an electrical railway vehicle, with the device having at least one fiber-optic sensor that is suitable for ascertaining the contact force between a contact wire and a contact strip of the pantograph, and a device for sensor control and sensor-signal processing connected to the sensor or sensors for separate-potential signal transmission.
Pantographs of modern high-speed railway vehicles should be embodied as actively-controlled pantographs with respect to the contact force between the contact strip of the pantograph and the contact wire, so that an optimum level of the quality of the energy supply and the wear at the contact point between the contact wire and the contact strip can be found and maintained, regardless of the relative movements between the railway vehicle and the contact wire, the aerodynamic forces on the pantograph components as stipulated by wind and vehicle speed, and the oscillatory behavior of the pantograph, the contact wire and the chain mechanism guiding the wire. While the force component of the true contact force resulting from the vehicle-speed-dependent air flow against the pantograph components can be determined through measurements and established as a parameter function for a control algorithm, the determination of the contact force F resulting from the mechanical action of the pantograph and the overhead-contact system requires a device that determines this contact force as close as possible to the aforementioned contact point, according to its magnitude and its point of entry, and, from the measuring location, which is located at a high-voltage level (e.g., 3 kV DC voltage; 15 kV or 25 kV AC voltage), further conducts contact-pressure-equivalent signals to internal vehicle evaluation devices, which are set at the opposite potential. The term xe2x80x98contact force Fxe2x80x99 refers hereinafter to this component of the true contact force between the contact wire and the contact strip, as results from the mechanical action of the pantograph and the overhead-contact system.
A generic device for determining the true contact force between a contact wire and a pantograph is described in U.S. Pat. No. 5,115,405 A. Here, a fiber-optic force sensor is mounted to the contact strip, the sensor being connected, via optical fibers (and therefore separated electrically in potential and being extensively independent of electrical and magnetic interference fields), to an internal vehicle device that supplies the sensor with light and receives its contact-force-dependent signal. The force sensor comprises an optical fiber that is clamped in spring-loaded fashion beneath the shoe that is in contact with the contact wire, and between the shoe and its holding device. A contact force that acts on the shoe leads to the deformation and micro-bending of the clamped optical fiber, altering its light-transmitting properties. This device is intended to recognize the overstepping of an upper and/or a lower threshold value of the true contact force between the contact strip and the contact wire, which is dictated, for example, by the impact of wind; the device is further intended to correct the contact force by means of an electronic-pneumatic command device and a pneumatic damping-compensation control element.
This device appears to be well-suited for detecting and signaling the overstepping of contact-force threshold values. This arrangement is, however, completely unsuitable for an effective measurement of a contact force within a specific force range, as is necessary for an active control of the contact force or the true contact force of a pantograph, because the fiber-optic force sensor has a very low signal/noise ratio, and a sufficiently precise, continuous determination of measured values is impossible. This sensor does not permit a determination of the point of entry of the contact force at the contact strip. Because the arrangement extends over the entire length of the shoe, it has a significant spatial expansion and mass, which can have a negative impact on the oscillatory and aerodynamic behavior of the pantograph.
The technical embodiment appears to be too sensitive to the types of stresses that are inevitable in the assembly, maintenance and transport of a pantograph. Because the temperature dependency of the light-transmitting properties changes with the degree of mechanical stress of an optical fiber, an effective compensation of this temperature dependency is scarcely possible. The continuously-changing mechanical stresses and deformities to which the optical fiber of this force sensor is subjected limit the service life of the fiberoptic sensor, thereby offering no guarantee of reliable device operation.
The patent publication EP 0 697 304 A2 discloses a device for measuring the contact force for an actively-controlled pantograph, in which a load recorder that measures in analog fashion and must cooperate with further length-measuring sensors to influence the action of two separately-operating vertical-lifting drives, by way of a control unit, is disposed beneath a pin-type insulator that supports the pantograph head and is disposed on a structure that swings out vertically, or the insulator is associated with the shoe. This load recorder should also be able to be constructed with the use of optical fibers; no further details are offered about the structure, arrangement and function of these fibers. At least in the arrangement of the load recorder beneath the pin-type insulator, considerable difficulties arise with respect to determining the magnitude of the contact force, because wind and mass forces acting between the points of contact and measurement affect the measurement result. It appears that the size of the load recorder, which can be seen from the drawings, makes it impossible to arrange the detector near the shoe, because this would have a negative impact on the oscillatory and aerodynamic behavior of the pantograph. It is not possible to ascertain the point of entry of the contact force at the contact strip using this load recorder.
German Patent Publication DE 195 18 123 C2 discloses a more detailed description of a device having a special optical-fiber sensor, with which mechanical pressure forces can be measured within the scope of rail technology, for example in rail-mounted axle-counting devices. This sensor has an inside tube and an outside tube, which is coaxial to the inside tube, is divided in the longitudinal direction of the tube and forms two contactless half-shells. A glass fiber that conducts light waves is embedded in helical fashion into an elastic mass between the inside tube and the outside-tube shells, and experiences a reversible bending in a certain bending-radius range during a one-sided, mechanical pressure stress of the sensor, in which the two half-shells of the outside shell are moved toward one another; this bending measurably damps an optical signal that passes through the glass fiber. This type of sensor has a complex design. It is only suitable for one stress direction, cannot be integrated as a structurally self-supporting component into the pantograph, and would be destroyed in the event of mechanical overstressing. The variable mechanical stress and deformation of the optical fiber of the sensor reduce the effectiveness of temperature-compensation measures, and likewise lead to a limitation of the service life and operating reliability. Thus, a sensor of this type appears to be unusable for measuring the contact force at a pantograph for the purpose of active pantograph control.
A further device for measuring the contact force for an actively-controllable pantograph is proposed in the German patent publication DE 195 40 913 C1. In this case, a force sensor is intended to be disposed at a telescopic strut that supports a contact strip, and an acceleration sensor is to be disposed at the rocker of a single-arm pantograph, the rocker supporting two parallel contact strips. The two sensor signals are supplied to the inputs of a control device, which initiates special torsion actuators that are disposed around the axis between the lower arm and the upper arms of the single-arm pantograph, and, in addition to the conventional lifting device of the pantograph, set the contact force of the contact strips at the contact wire. From the drawings, it can be assumed that the contact force of the contact strip at the contact wire is determined by way of a path measurement from the spring deflection of the telescopic strut, or a force sensor measures the force transmitted by the telescopic strut. A disadvantage is the relatively large distance between the sensors and the actual contact point between the contact wire and the contact strip, because mass and wind forces occurring between the contact point and the respective sensor influence the measurement results, and can skew the control result. This document, however, offers no representation of the embodiment and operating principle of the sensors.
The French magazine publication of xe2x80x9cDelfosse, P; Sauvestre, B.: Measurement of contact pressure between pantograph and catenary,xe2x80x9d Revue Gxc3xa9nxc3xa9rale des Chemnins de Fer, Vol. 1, No. 6, 1983, pp. 497-506xe2x80x3 proposes a device for measuring the contact force serving in the evaluation of the status of an overhead-contact system comprising a contact wire and a chain mechanism, and employs a specially-designed measuring-current pantograph, in which each of the two parallel contact strips is replaced by a special contact strip that is supported by two bending girders that allow the contact force acting on each contact strip to be determined by means of strain gauges and potentiometric measurement, according to both the magnitude and the point of entry of the pressure, from the torques exerted on the bending girders, which are clamped on one side. The sensors disposed in the region of the pantograph rocker and set at a high-voltage potential must be separated by potential, and with a high machinery outlay, from their energy-supply, signal-processing and control devices that are integrated into the vehicle control, and protected through special measures against electrical and magnetic interference fields. The illustrated arrangement of the force sensors has no protection against mechanical and weather influences. A structural adaptation of this device for a pantograph that is suitable for the operational use appears complicated and costly; the additional mass of the bending-girder arrangement would negatively affect the oscillatory and aerodynamic behavior of the pantograph. Therefore, this type of device with these particular sensors is not even considered for the active control of a real pantograph, or the measurement of its contact quality.
EP-0 363 623 discloses a device for measuring the contact force between a contact wire and a pantograph of an electrically-powered vehicle, namely an electrical railway vehicle, having at least one fiber-optical sensor that is suitable for ascertaining the contact force between a contact wire and a contact strip of the pantograph; a device for controlling the sensor and processing the sensor signals; and a fiber-optic device that connects these devices for separate-potential signal transmission, with two resilient deformation bodies being disposed between a base body of the contact strip and a contact strip support and fixedly connected to the two. These deformation bodies support the contact strip, and each has an integrated fiber-optic sensor that detects deformations in the deformation body that are equivalent to a contact force, and signals them to the aforementioned device for sensor control and sensor-signal processing, in which the detected deformations are converted into contact-force-equivalent signals and outputted, or from which desired commands that are equivalent to changes in contact force are derived and outputted.
It is the object of the invention to provide a solution for a generic device that utilizes the advantages that are generally anticipated in the state of the technology for fiber-optic sensors having fiber-optic signal transmission for a force measurement at a high voltage, while avoiding the disadvantages of these sensors. The fiber-optic sensor of such a device should be disposed as close as possible to the actual contact point between the pantograph and the contact wire, and be able to measure the forces occurring between the components directly and without large relative paths between the components. The solution is intended to permit a shape, size, mass and arrangement of the measuring device with the fiber-optic sensor such that the oscillatory and aerodynamic behaviors of the pantograph remain extensively undisturbed. This device is intended to permit a determination of the contact force, both according to its magnitude and its point of entry at the shoe, and generate and output signals that are equivalent to a contact force, or generate and output commands that change the contact force, the signals and commands being applicable for an actively-controlled pantograph.
These above objects generally are achieved according to the present invention by a device for measuring the contact force between a contact wire and a pantograph of an electrically-powered vehicle, particularly an electrical railway vehicle, with the device having at least one fiber-optic sensor that is suitable for ascertaining the contact force between a contact wire and a contact strip of the pantograph, and a device for sensor control and sensor-signal processing that is connected to the sensor or sensors for separate-potential signal transmission; and wherein: two resilient deformation bodies are disposed between a shoe and a base body of the contact strip and are fixedly connected to the shoe and the base body, with the deformation bodies supporting the shoe; and each deformation body having an integrated fiber-optic reflex sensor that detects contact-force-equivalent deformations of the deformation body and signals the deformations to the device for sensor control and sensor-signal processing. Advantageous modifications and embodiments ensue from the further description.
With a device of the invention, it is possible to attain such contact-force-equivalent signals, or to derive from them commands that are equivalent to a change in contact force, and output these commands, as needed for a continuous control of a pantograph by means of its lifting drive and its control device; here, the advantages that are known in principle for fiber-optic sensors and their electrical, separate-potential signal transmission are used.
The solution according to the invention permits the ascertaining of the contact force, both according to its magnitude (through summation of the signals of the two fiber-optic sensors supporting a contact strip or a shoe) and its point of entry (through comparison of the signals from the individual forces of the two fiber-optic sensors supporting a contact strip or a shoe, and the computational application of lever principles). Because it is known that contact-force peaks regularly occur where the contact wire and the chain mechanism are suspended at the catenary supports, the knowledge about the changing point of entry of the contact force can be used in a control algorithm for recognizing the zigzag course of the contact wire and determining the sequence frequency of the catenary supports, as well as its first and second derivations, and for correcting the contact force in order to prevent the aforementioned contact-force peaks.
A significant advantage of the invention is that the devices of the invention can easily be modified for applications in other technical fields in which forces, but also pressures and accelerations, between components set at a high-voltage potential are to be measured. In contrast to conventional measuring methods employing strain gauges and the potentiometric formation of measured values, or piezoelectric force recorders, the outlay for the measuring arrangement and for the signal conversion, transmission and processing can be greatly reduced.
Another notable advantage of the invention is that the components of the measuring device with the fiber-optic sensor are embodied and assembled to have the smallest-possible dimensions and mass, and can be integrated, so as to transmit a force, between the pantograph components.
A further advantage is that the embodiment of the components of the measuring device that are necessary for the devices of the invention allows them to be produced inexpensively and with reproducible properties.
A further advantage of the concept of the invention is that, for example, in the variation illustrated in the exemplary embodiment, only very small changes are necessary in the design of pantograph types that have already been thoroughly tested and are in use, so an inexpensive retrofitting of devices according to the invention can be considered for numerous electrical railway vehicles in operation.
The contact-force-equivalent signals obtained with the devices of the invention are also suitable for special measuring purposes with which, for example, the contact quality of a pantograph can be checked, or the status of an overhead line and its chain mechanism in a path segment can be assessed.